(a) Field of the Invention
The present invention relates to a system and method for mobile communications. More specifically, the present invention relates to a system and method for mobile communications which remove blanket areas of communications using a mobile repeater.
(b) Description of the Related Art
Conventional mobile communications systems comprise base stations (BS), base station controllers (BSC), a mobile switching center (MSC), and mobile stations (MS).
The BSs communicate with the MSs using predetermined frequencies, and each BS has a predetermined communications area. Therefore, a plurality of BSs is arranged in a suitable manner so that communications areas of adjacent BSs partially overlap to create a large area where mobile communications can take place.
However, even though with the above-mentioned arrangement an entire city can be covered, blanket areas where no communications are possible come to be formed in underground spaces of large buildings, interior spaces of skyscrapers, etc. As a result, communications service can not be provided to users in such blanket areas.
To solve the formation of the blanket areas, radio frequency (RF) repeaters are provided in those areas.
FIG. 1 is a schematic diagram of a conventional in-building repeater used in code division multiple access (CDMA) communications.
As shown, the in-building repeater comprises duplexers 11 and 16; low noise amplifiers 12 and 17; pre-amplifiers 13 and 18; intermediate frequency (IF) modules 14 and 19; surface acoustical wave (SAW) filters 1 and 4; mixers 2 and 3; and power amplifiers 15 and 20.
An operation of the in-building repeater of the above configuration will now be described.
When RF signals are received from a BS through a directional antenna 10, the received signals are transmitted to the low noise amplifier 12 in the transmission direction through the duplexer 11. The low noise amplifier 12 and the pre-amplifier 13 then amplify the signals, and the IF module 14 converts the amplified signals into intermediate frequency signals. After the signals are output from the IF module 14, noise is removed from the signals in the SAW filter 1, and then converted into RF signals in the mixer 2. The converted signals are amplified in the power amplifier 15, pass through the duplexer 16, then are radiated through in-building antennas or leakage coaxial cables.
On the other hand, the RF signals transmitted from a MS of a subscriber are received through the in-building antennas or leakage coaxial cables, passed through the duplexer 16, and amplified by the low noise amplifier 17 and pre-amplifier 18. The RF signals amplified by the pre-amplifier 18 are converted into IF signals in the IF module 19, and signal noise is removed through the SAW filter 4, after which the signals are converted into RF signals through the mixer 3. The converted RF signals are amplified by the power amplifier 20, passed through the duplexer 11, then radiated from the antenna 10 to be transmitted to the BS.
The in-building repeater using the conventional antenna can be used only on a single floor or one particular space of a building. Therefore, in order to radiate the waves to many floors, the leakage coaxial cables are utilized.
However, since waves are radiated only along the paths where the leakage coaxial cable lies in the conventional in-building repeater, a cable of substantial length must be used in large buildings. As a result, transmission loss occurs as signals travel the distance of the cable. In addition, installation of the cable becomes complex with the increased length of the same, and the costs involved in installing the lengthy cable are high.
Optionally, a light dispersion antenna is used which converts the RF signals into light waves and radiates the light signals to the blanket areas in a building.
FIG. 2 is a schematic diagram of an in-building repeater using a conventional light dispersion antenna.
As shown, the repeater comprises duplexers 36 and 40; low noise amplifiers 22 and 39; mixers 23, 25, 31, and 34; filters 24, 26, 29, and 32; light transmitters 27 and 38; light receivers 28 and 36; a light dispersion antenna 41; and power amplifiers 35 and 37.
The operation of the repeater using the light dispersion antenna is similar to that of the previously described repeater. But in contrast, the RF signals are converted into light signals to be transmitted through optic cables, and the light signals are radiated to the blanket areas using the light dispersion antenna 41.
However, the installation of the repeater using the optic cables and light dispersion antenna involves great costs.
It is an object of the present invention to provide a system and method of mobile communications for reducing blanket areas in a building at a low cost.
In one aspect of the present invention, a mobile communications system comprises a base station (BS) transmitting and receiving signals by a predetermined serving frequency signal; a donor module coupled to the BS, the donor module converting output signals of the BS into intermediate frequency (IF) signals and outputting the converted signals to a path, and the donor module converting the IF signals provided from the path into serving frequency signals and transmitting the converted serving frequency signals to the BS; and a plurality of remote modules receiving output signals of the donor module through the path, and converting the signals into the serving frequency signals and outputting the serving frequency signals to a mobile station (MS) within a blanket area, and the remote modules converting the signals into IF signals and outputting the signals to the donor module through the path.
The donor module comprises a first duplexer performing bi-directional communications with the BS; a transmitter converting radio frequency (RF) signals provided through the first duplexer into IF signals, and amplifying and outputting the signals; a second duplexer transmitting the signals of the transmitter to a rigid (RG) cable, the second duplexer receiving IF signals through the RG cable; a receiver converting IF signals transmitted to the second duplexer into RF signals and transmitting the signals to the first duplexer; and a power controller detecting a signal level of the receiver and controlling the power of the transmitter and receiver.
The transmitter comprises a first low noise amplifier amplifying the RF signals provided through the first duplexer; a first mixer converting the RF signals into IF signals; a first surface acoustic wave (SAW) filter filtering output signals of the first mixer to obtain desired IF signals; a first variable attenuator performing power control on output signals of the first SAW filter according to external control signals; a first power amplifier performing power amplification on output signals of the first variable attenuator; a frequency shift keying (FSK) modulator outputting FSK modulated signals; a second variable attenuator controlling power according to control signals of the power controller; a first amplifier amplifying signals of the second variable attenuator; a first low pass filter performing a low pass operation on signals of the first amplifier; and an adder adding signals of the first low pass filter and the first power amplifier, and outputting resulting signals.
The receiver comprises a second SAW filter passing desired IF signals among the IF signals transmitted to the second duplexer; a second low noise amplifier amplifying output signals of the second SAW filter; a second mixer providing status control signals to the second low noise amplifier according to control of the power controller; a third variable attenuator performing power control on output signals of the second mixer according to control of the power controller; a third mixer converting signals of the third variable attenuator into RF signals; a third SAW filter passing desired RF signals among output signals of the third mixer; and a second power amplifier performing power amplification on output signals of the third SAW filter and outputting resulting signals to the first duplexer.
Each of the remote modules comprises a first duplexer performing bi-directional communications with the donor module; a transmitter converting IF signals provided through the first duplexer into RF signals, and amplifying and outputting resulting signals; a second duplexer transmitting signals of the transmitter to external blanket areas and receiving RF signals transmitted from an external MS; a receiver converting the RF signals provided to the second duplexer into IF signals and transmitting converted signals to the first duplexer; and a power controller detecting signal levels of the receiver and performing power control of the transmitter and receiver.
In another aspect of the present invention, a mobile communications system comprises a repeater transmitting and receiving signals to/from external base stations (BS) using predetermined frequency signals; a donor module coupled to the repeater, the donor module converting output signals of the repeater into intermediate frequency (IF) signals and outputting the signals to a rigid (RG) cable, and the donor module converting the IF signals provided from the RG cable into serving frequency signals and transmitting the signals to the BS; and a plurality of remote modules receiving output signals of the donor module through the RG cable, and converting the signals into serving frequency signals and outputting the signals to a mobile station (MS) within the blanket area, and the remote modules converting the signals provided from the MS into IF signals and outputting the signals to the donor module through the RG cable.
In a still further aspect of the present invention, a mobile to communications method comprises the steps of transmitting and receiving signals using predetermined frequency signals at a base station (BS); converting output signals of the BS, coupled to a donor module, into intermediate frequency (IF) signals, and performing power control on the signals and outputting the signals to a path; receiving output signals of the donor module through the path at each of a plurality of remote modules, and converting the signals into serving frequency signals and outputting the converted signals to a mobile station (MS) within a blanket area; converting signals received from the MS into intermediate frequency (IF) signals at the remote modules and outputting the signals to the donor module through the path; and converting IF signals received from the remote modules through the path into serving frequency signals at the donor module and transmitting the signals to the BS.